docs: def load_umatrix(self, filename):
          """Load the umatrix from a file to the Somoclu object.
  
          :param filename: The name of the file.
          :type filename: str.
          """
  
          self.umatrix = np.loadtxt(filename, comments='%')
          if self.umatrix.shape != (self._n_rows, self._n_columns):
              raise Exception("The dimensions of the U-matrix do not "
                              "match that of the map")